Radiometric measuring systems have served for many years as contactless measuring methods for process measurements. They are applied where process parameters, such as e.g. fill level of a medium in a container, an interface and/or a density of the medium, have to be measured under difficult conditions, such as e.g. extreme temperatures and pressures. Known radiometric measuring systems include, typically, a radioactive radiator and a detector attached at, or on, a container or pipe, as well as also including an evaluation unit. Measuring methods associated therewith are likewise known per se. Especially in the chemicals industry, radiometric measurements are indispensable for difficult processes.
On the other hand, exactly in the plants of the chemical industry, the integrity of pipes and containers and their connections is very important and, therefore, must be examined from time to time. In the context of a non-destructive, materials testing of pipelines, weld seams and pressure vessels, gammagraphy is frequently applied, in the measuring methods of which, radioactive radiators and detectors are likewise used. When such a gammagraphy measurement is performed in proximity to a radiometric measuring system, interferences with the radiometric measuring system can arise, stemming from the radioactive radiator used for the gammagraphy, so that errors are introduced into the measurements of the process variables.
In one of the methods commonly used currently, for suppressing interferences from gammagraphy, the affected radiometric measurement in the vicinity of the gammagraphy inspection is stopped, or interrupted, before the gammagraphy is begun, and the last measurement of the process variables is retained, i.e. stored, and, in effect, frozen. During the gammagraphy measurement, the measurement of the process variables is at rest in the radiometric measuring system and is not available for process control. Upon termination of the gammagraphy inspection, the radiometric measuring system is turned on again, and the measurement of the process variables resumed. The disadvantages of this method are evident: Either the process variable registered by the radiometric measuring system can no longer be measured and monitored, and that can lead to serious effects in the process control; or a gammagraphy measurement must be forsaken, thus no inspection of pipe and container walls and weld seams, when no interruption of the registering of process variables is allowable, this being especially the case for radiometric measurements of the fill level of a medium in a container, where pumps are controlled on the basis of the current fill level measurement. The other alternative, of shutting down the affected branch of the process, is likewise problematic for most plant operators.